[V2] handleChange should accept any value

[blueberry6401]

🐛 Bug report

Current Behavior

I'm using Formik on React-native and Typescript.
For example, I have only one field of type number:

type MyFieldValues = {
  val: number,
}

On input handleChange
formikProps.handleChange('val')(newVal as number);

Got this: Error:(100, 46) TS2345: Argument of type 'number' is not assignable to parameter of type 'string | ChangeEvent'.

Expected behavior

handleChange should accept any value type like setFieldValue does.

Your environment

Software	Version(s)
Formik	2.0.6
React	16.9.0
TypeScript	3.6.3
Browser
npm/Yarn
Operating System	Mac 10.15.1

[elkinjosetm]

What's the update on this bug?

[blueberry6401]

Shouldn't this be fixed? I still use patch-package to handle this tiny bug.

[johnrom]

I explain the resolution for this in depth here: #3013 (comment)

Unfortunately, we need to upgrade TS to TS4 to actually solve this problem, so this will probably be a major version update.

Edit: I do think we can accept any (or unknown and cast to any, so we can properly check for Events) in handleChange for now, but when we eventually add real typings that will be a breaking change. @jaredpalmer I think we can change this to any in v2, so the breaking change can occur in the jump from v2 to v3.

[JulianKingman]

The problem is not only types and typescript, but also functionally it only accepts strings or events. The types are actually correct, in that if you pass anything else, you run into this error: #1667 (dupes: #2942, #1973).

Here are some closed PR's that try to address the above issue:
https://github.com/formium/formik/pull/2305/files
https://github.com/formium/formik/pull/1669/files (#2255 was supposed to carry this on, but looks like the type part didn't make it)
https://github.com/formium/formik/pull/3039/files

Based on @johnrom 's comment here, it seems that setFieldValue should be used instead of handleChange? If that's true, then perhaps we just need a documentation update for the migrating-v2 guide page.